1. Horticulture Science Lesson 21 Understanding Growing Media Components

2. Interest Approach
Have the students collect a sample of soil from their yards. Students should try to identify the components they find in the soil such as bark, leaves, stones, insects, weeds, and seeds. Next, lay out samples of a potting mix. Challenge the students to find similar components in the potting mix. Ask the students to then list the components of a growing medium. Next, lead the students in a discussion on what actually makes a soil.

3. Student Learning Objectives
Describe the components of soil.
Appraise the components of a soilless mix.
Evaluate the advantages and disadvantages of soilless medium.

4. Terms
amend
bark
calcined clay
clay
coir
humus
inorganic
loam

5. Terms mineral matter organic matter pasteurization peat moss perlite
plastic foam
rock wool

6. Terms
sand
silt
soil
soilless mix
sterilization
tilth
vermiculite

7. What are the components of soil?
Soil is the outer portion of the Earth’s crust that supports plant growth.
Soil varies from one location to another based on the parent material or rock.
As parent material is weathered or worn away, small bits accumulate to form soils.

8. What are the components of soil?
Climate is also a factor in soil formation.
Soils are often distinguished by the amount of mineral matter found in them.
Mineral matter is the inorganic or non-living substance that comes from weathered rock to form soil.
The three types of mineral matter found in soil are sand, silt, and clay.

9. What are the components of soil?
1. Sand is the largest soil particle.
Physically separate and see individual grains of sand.
Sand particles create large pore spaces that improve aeration.
Water flows through the large pore spaces quickly and considered to be well-drained.

10. What are the components of soil?
Sandy soils lack the ability to hold nutrients and are not fertile.
Soils that contain sand particles feel gritty to the touch.

11. What are the components of soil?
2. Silt is the mid-size soil particle.
It has good water-holding ability and has the ability to hold nutrients.
Silt feels like flour when dry and smooth like velvet when moist.
Silt is a particle of soil that is produced by the action of water breaking down minerals.

12. What are the components of soil?
3. Clay is the smallest soil particle and has the ability to hold both nutrients and water that can be used by plants.
It creates very small pore spaces, resulting in poor aeration and poor water drainage.
Clay forms hard clumps when dry and is sticky when wet.

13. What are the components of soil?
Sand, silt, and clay, the three minerals found in soil, make up about 45% of soil composition.
When there are equal amounts of sand, silt, and clay present in soil, it is called a loam.

14. What are the components of soil?
An average soil is composed of 5% organic matter.
Organic matter is the accumulation of decayed or partially decayed plants and animals, roots, and living organisms.

15. What are the components of soil?
Humus is organic matter that has reached a point of stability where it will break down no further.
It is from plant leaves, roots, and stems.
Soils with high organic matter, tend to be dark in color.
Organic soils are more productive than soils with low organic matter content because the organic matter contributes to soil fertility.
Additional advantages to organic matter include improved aeration and waterholding capacity.

16. What are the components of soil?
Abundant life can be found in soil in the form of earthworms, insects, bacteria, fungi, and other organisms.
Bacteria and fungi have an important role in the soil; they break down organic matter and release nutrients.

17. What are the components of soil?
Earthworms, ants, crawfish, moles, and other organisms improve the soil tilth, which is the ease at which soil can be worked.
These organisms create openings in the soil as they tunnel, which enhances drainage and improves air exchange.
Roots of living plants contribute to the soil mass.

18. What are the components of soil?
The remaining 50% of soil is composed of air and water.
The air and water occupy pore spaces.
A typical soil might have 25% air and 25% water.
However, these percentages fluctuate as soils dry out or are soaked by rain.

19. What are the components of a soilless mix?
Soil-based growing medium are being used less often in the production of potted horticultural crops, because it has become more difficult for growers to find uniform mineral soil with a favorable pH in addition to good structure and texture.
For potted plants, producers are using soilless mixes.

20. What are the components of a soilless mix?
A soilless mix is a combination of organic and inorganic substances in which plants are grown.
A soilless mix does not contain mineral soil.
Different materials are used in soilless medium.

21. What are the components of a soilless mix?
Peat moss is one of the most widely used components of soilless medium.
It is an organic material dug from peat bogs in Canada, Michigan and Florida.
Peat moss has great moisture and nutrient-holding capacity.
Because peat moss has light bulk density, good moisture-holding ability, good airspace qualities for the exchange of gases, adequate cation-exchange capacity, and a stable pH that is usually between 3.5 and 4.5, it is often used to amend soil.

22. What are the components of a soilless mix?
Perlite is white in color and comes from heat-treated volcanic rock.
Perlite is a good lightweight substitute for sand.
It is stable and sterile.
Perlite also has little cation-exchange capacity, a pH of 7.5, and provides good water drainage and aeration.
Perlite contains fluorides that cause leaf damage to some monocotyledon plants including freesias, dracaenas, and spider plants.

23. What are the components of a soilless mix?
Vermiculite comes from the mineral mica and is shiny brown in color.
It is a lightweight material and can be easily compressed.
It has high moisture-holding capacity and aeration.
Vermiculite is available in different grades, ranging from a fine grade for use with seeds to a coarse grade measuring more than 1/4 inch in diameter.

24. What are the components of a soilless mix?
Vermiculite has a good cation-exchange capacity and a neutral to slightly alkaline pH (6.3 to 7.8).
It also provides small amounts of calcium, magnesium, and potassium for plant use.
African vermiculite has high potassium content and is very lightweight.
Vermiculite is often used as the media for germinating seeds.

25. What are the components of a soilless mix?
Perlite & Vermiculite

26. What are the components of a soilless mix?
Coir is made from waste products of the coconut industry and is, therefore, considered a renewable resource.
Its characteristics are similar to those of peat moss.
It has high water-holding ability and excellent drainage.
Another advantage to coir is that it encourages faster rooting of plants.
A disadvantage is that it has high salt content because coconuts grow near the sea.

27. What are the components of a soilless mix?
Bark from trees is obtained as a byproduct through the timber industry.
It is relatively inexpensive, and thus lowers the cost of the growing medium.
The most widely used bark in the greenhouse industry is pine bark.
Bark that is ground into fine pieces is the most useful because of its uniform qualities.
Bark improves the moisture-holding ability and aeration of a mix.
After peat moss, bark is the second-best organic-matter medium component.

28. What are the components of a soilless mix?
Sand is found naturally and is a result of the wearing of rock.
Sand is heavy and has a high bulk density that provides solid support for larger plants.
It improves water drainage and aeration when used with soil.
The sand particles can actually reduce aeration in peat or bark mixes by filling pore spaces created by the peat or bark.
The pH of sand is between 7.5 and 8.5.
If used, sand must be sterilized to destroy Pythium and Rhizoctonia disease organisms.

29. What are the components of a soilless mix?
Plastic foam flakes or beads (the most common is Styrofoam) are a synthetic polystyrene material.
Plastic foam is very lightweight and stable.
While it provides good drainage and aeration, plastic foam lacks cation-exchange capacity and water-holding abilities; it also has a neutral pH.
In addition, plastic foam tends to float to the surface of growing media.

30. What are the components of a soilless mix?
Calcined clay is clay aggregate heated to form a hard, stable particle.
It has a high bulk density.
Calcined clay improves water drainage and aeration in a medium.
It also has some cation-exchange capacity.

31. What are the components of a soilless mix?
Rock wool is a human-made material from an igneous rock: basalt.
The rock is heated to 2700° F; once liquefied, it is spun into fibers similar in appearance to cotton candy.
Rock wool is used extensively in hydroponic operations.
Rock wool cubes are used in plant propagation.
Granular forms of rock wool are used as a medium component.
Rock wool has good water-holding capacity and good aeration.
It is slightly alkaline and has a low cation-exchange capacity.

32. What are the advantages and disadvantages of soilless medium?
Horticulturists compare the advantages and disadvantages of growing medium.
Selecting the best material for a particular crop is important to the success of a crop.
One reason soilless mixes have grown in popularity is because they have a number of advantages.

33. What are the advantages and disadvantages of soilless medium?
1. Soilless mixes are uniform in components, texture, or nutrients.
2. Soilless mixes are sterile.
Sterilization is a process that eliminates all disease organisms, insects, or weed seeds.
Mineral soil contains disease organisms, insects, or weed seeds.
If mineral soil is used in a growing medium, it must be pasteurized.
Pasteurization is the process of heating soil to 180°F for 30 minutes to kill the harmful diseases, weed seeds, and insects.

34. What are the advantages and disadvantages of soilless medium?
3. By adjusting the amounts of the various components of a soilless media, drainage and moisture-holding capacity can be altered.
4. A grower can personally mix the combination of components exactly to what he or she needs for a particular crop.
5. Soilless mixes are easier to ship and move because they are lightweight.

35. What are the advantages and disadvantages of soilless medium?
Some disadvantages to soilless medium exist.
Fertilizers need to be added more frequently to the soilless medium because soilless medium have low cation-exchange capacity.
By comparison, mineral soil contains and holds many minor nutrients.
2. When plants are grown outdoors, the wind can blow dry pots over because the mix is very light.

36. Review/Summary What are the components of soil?
What are the components of a soilless mix?
What are the advantages and disadvantages of soilless medium?